The present invention relates to a process for producing a semiconductor laser having several independent wavelengths and to a laser obtained by this process. Its application is in the field of optical telecommunications.
The technical field of the invention is that of so-called double heterostructure semiconductor lasers having a junction in the form of a tape or ribbon. A double heterostructure is constituted by a stack of semiconductor layers deposited on a monocrystalline substrate. Starting from the substrate, there is generally a confinement layer, an active layer, a second confinement layer and a contact layer, covered by a metal coating.
For lasers emitting between 0.8 and 0.9 .mu.m, these layers are made from the alloy Ga.sub.1-x Al.sub.x As and the substrate is made from GaAs. For lasers emitting between 1.3 and 1.65 .mu.m, the lasers are formed from Ga.sub.1-x In.sub.x As.sub.1-y P.sub.y and the substrate is of InP.
The continuous operation of these lasers is obtained by reducing the active part to a ribbon about 10 microns wide and 300 microns long. This ribbon is obtained by proton bombardment on either side of the area which has to remain active.
The main field in which semiconductor lasers are used is that of optical fibre telecommunications systems. In order to increase the transmission capacity of such systems, wavelength multiplexing is most frequently used. The normally adopted solution consists of connecting lasers emitting at different wavelengths to a single optical fibre, via an optical multiplexer.
The invention aims at providing a process for producing a laser which, itself, is able to emit several wavelengths, in such a way that such a laser can be coupled to the same optical fibre, without a multiplexer.
U.S. Pat. No. 4,318,058, particularly with respect to its FIG. 4, describes a device having several lasers separated by grooves. These lasers have in common a substrate, a confinement layer and an active Al.sub.x Ga.sub.1-x As layer, in which the proportion x is not the same for the different lasers.
This patent also describes a process for producing such a device. In order to obtain an active layer of varied composition, use is made of a device comprising a mask having a slot, through which molecular epitaxy is performed. This leads to an active layer, whose percentage x can, for example, be continuously increasing.